This research is designed to investigate the possible relationships between bacterial interference due to viridans streptococci and type-specific nasopharyngeal M protein antibodies in the pathogenesis in the recovery from infection of the upper respiratory tract due to hemolytic streptococci. This research will be accomplished in the following manner: First, to detect changes in the bacterial flora of the pharynx accompanying acquisition of group A streptococci associated with a streptococcal infection or the carrier state; second, by determining whether a change in the numbers or inhibiting quality of streptococcus viridans in the bacterial flora is associated with (a) acquisition of, or (b) disappearance of hemolytic streptococci associated with a streptococcal infection; third, by testing in vitro for bacterial interference by viridans streptococci on strains of Group A streptococcus etiologic for streptococcal infections; and fourth, to test simultaneously for local, type-specific streptococcal M protein antibodies in nasopharyngeal secretions. By simultaneously investigating M protein antibodies and bacteriostatic effects it will be possible to evaluate the relative role of each in the pathogenesis and recovery process of streptococcal infections.